Various contactless rotary position sensors and potentiometers have been proposed for providing a linear output response. Contactless devices, of course, are advantageous over similar resistive-type devices because they have a considerably longer lifetime. Although contactless potentiometers which utilize a rotating permanent magnet section and a sensing element were previously known, these prove to have several decided disadvantages. The major disadvantages of such prior devices being that they generally required that the magnet or the sensing element, or both, be formed with a special precalculated shape in order to obtain the desired linearity. This obviously made these devices relatively costly to produce and, in addition, the shapes required could result in unduly increasing their size. Examples of such devices are shown in U.S. Pat. No. 3,335,384, which issued Aug. 8, 1967, to Herbert Weiss, and in U.S. Pat. No. 3,958,203, which issued May 18, 1976 in the name of Victor M. Bernin, and which is assigned to the assignee of the present invention.
U.S. Pat. No. 3,988,710, which issued Oct. 26, 1976, to Edward Frank Sidor and Frank B. Desio, and which was assigned to the assignee of the present invention, discloses a new type of contactless linear rotary position sensor, or potentiometer, which avoids the above noted deficiencies of other prior devices and which provides excellent linearity, is of relatively low cost and of relatively small size. In addition, the linear rotary devices of the Sidor and Desio patent has other decided advantages in that it is highly resistant to shock and vibrations and it is capable of operating over a temperature range of -50.degree. C to as high 200.degree. C, or even higher, depending on the Curie point of the magnetic material that is employed.
It was found that the linear device of the Sidor and Desio patent, however, while possessing all of these excellent characteristics and while being capable of operating over a large temperature range and at high temperature, did exhibit an undesirable amount of temperature dependency for certain applications in that a plot of the output voltage vs. the degrees of rotation of the permanent magnet resulted in a graph that had a slope that varied appreciably as a function of the ambient temperature. For example, a plot of the output voltage vs. degrees of rotation of the magnet, while remaining linear for one sample over the entire temperature range from -50.degree. to 130.degree. C, had a slope variation as a function of temperature that was found to be excessive for certain applications.
The present invention is directed to an improved version of the basic linear device of U.S. Pat. No. 3,988,710 in which the above described undesirable slope variation as a function of temperature is greatly reduced. For example, when the sample device mentioned above was provided with the improvement of the present invention the slope variation of the plot of the output voltage vs. degrees of rotation of the magnet was found to be substantially constant from 25.degree. to 130.degree. C, while the slope at -50.degree. C varied only slightly from that measured at 25.degree. C. The sample device in question varied approximately 2.5 millivolts per degree of rotation of the magnet when it did not incorporate the improvement of the present invention, while the slope varied approximately only 1.0 millivolts per degree of rotation of the magnet over the same temperature range when the device was provided with the improvement of the present invention. It is seen, therefore, that the improvement of the present invention substantially reduces the temperature dependency of a sensor constructed in accordance with U.S. Pat. No. 3,988,710 over the operating temperature range of such a device.